The background description provided here is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventor, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Internal combustion engines combust an air and fuel mixture within cylinders to drive pistons, which produces drive torque. A coolant is circulated through the engine block and the cylinder head(s) of the engine, and the cooling is maintained at an approximate predetermined temperature during normal operation. This enables the engine to operate at a predetermined operating temperature which maximizes efficiency, and thus the fuel economy of the engine.
During a start-up of the engine when the engine is cold, it is important, particularly for optimizing fuel economy, to have the engine reach its normal operating as quickly as possible. This promotes more efficient combustion and, importantly, reduces fuel consumption during engine warm up. However, it is not possible to simply provide zero coolant flow for the entire engine during the warm up phase. This is because the various parts of a modern internal combustion engine do not heat up perfectly uniformly during engine warm up. It has been determined that with modern turbocharged internal combustion engines, a component known as the integrated exhaust manifold (IEM), which flows exhaust gasses into the turbocharger, is typically the component that warms most rapidly during engine warm up from a cold start. So very shortly after initial startup, at least some small degree of coolant flow will need to be circulated through the IEM to prevent boiling of the coolant within the coolant jacket of the IEM. Preventing coolant boiling is important because coolant boiling will stress the metal of the IEM. However, simply flowing coolant through all parts of the engine in a relatively uniform flow will serve to pull heat out of the metal components making up the combustion chamber area, and more specifically from the cylinder head and the engine block proximate to the combustion chamber, and thus serve to lengthen the time that it takes the engine to reach its normal operating temperature. This also results in a reduction in fuel economy during the warm up phase.
The challenge is therefore how to manage the flow of coolant through select parts of the engine in a manner that prevents coolant boiling in those areas of the engine that typically heat up most rapidly, but which still does not pull heat out of the metal components of the engine in proximity to the combustion chambers of the engine. Addressing this challenge will enable improved fuel economy to be achieved during the warm up phase of the engine.